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The Huerfano-Cucharas Irrigation Company May 12, 2009 (UPDATED May 22, 2009) Page 2 of 7 Background Agenda Item 17h The Company owns and operates the Cucharas No. 5 Dam and Reservoir. The Cucharas No. 5 Dam is located in northeastern Huerfano County on the Cucharas River, approximately 16 miles northeast of the City of Walsenburg. The Reservoir supplies imgation water to cultivated lands in southeast Pueblo County, north of the Huerfano River. The dam is a 145-foot high rock fill dam that has undergone several enlargements since the original construction in 1914. The Reservoir has a capacity of 35,395 acre-feet to the spillway crest elevation of 5766.0 feet, gauge height 120.5 feet. In May of 1987, while the Reservoir was full to the spillway crest, the dam developed extensive seepage along the toe abutments of the dam. Immediate action was taken to lower the water level and avoid complete dam failure. It was discovered that the upstream concrete facing on the rock fill dam had failed and was allowing large quantities of seepage flow to occur through the embankment. The water surface was lowered by notching the spillway. Portions of the concrete facing were repaired in 1987 and 1988; however, during initial filling, the Reservoir dam again began to seep and the Reservoir was drained to its present restricted gauge height of 100 feet or 7,500 acre-feet of storage. The storage restriction has remained in effect since 1988 and there is a deadline of October 1, 2010 imposed by the SEO either to rehabilitate the existing dam, replace it with a new dam or a zero no-storage restriction will be imposed followed by an order to breach the dam and remove the hazard it represents. The dam has performed adequately at the restricted level with only moderate increases in seepage flow at higher storage levels being recorded, but the spillway is inadequate and there remain unknowns concerning the condition of the embankment and foundation. In addition, the Reservoir has accumulated a large quantity of silt. The current silt level against the upstream face of the dam goes up to gauge height 80. There are two functioning 36=inch diameter outlet slide gates on the face of the outlet works having their inverts approximately eight feet below the existing silt level. A silt catchment fence and depressed rock basin around the outlet structure allows water to flow to the gates with minimal silt flow through the gates. Loan Feasibility Study Mike Graber, P.E., Applegate Group, Inc., prepared the Loan Feasibility Study titled "Cucharas Reservoir No. S Dam Rehabilitation Feasibility Study, " dated March 2009. The study was prepared in accordance with the CWCB guidelines and includes preliminary engineering design and cost estimates. Additional studies that have been performed in recent years include: 1. Feasibility study by URS Corporation evaluating replacing the existing dam with a new Roller Compacted Concrete Dam (RCC) downstream of the existing dam completed in September 2006. 2. "Evaluation of Yield from Cucharas No. 5 Reservoir" dated December 2005 by Lytle Water Solutions, Bruce Lytle, P.E. with a supplement completed in November 2006. 3. Storage capacity survey work completed in October 2002 — Clyde B. Young & Co.